The present invention relates to a three-dimensional object-forming method for forming an object of a three-dimensional shape with photosetting resin by casting the laser light to the resin.
A method has been used in recent years to form three-dimensional shapes, whereby the laser light is scanned to liquid photosetting resin and the obtained photoset layers of resin are laminated to assume a desired three-dimensional shape.
An example of the conventional three-dimensional object-forming method referred to above will be described with reference to FIG. 6. FIG. 6 is a schematic structural diagram of a three-dimensional object-forming apparatus which carries out the three-dimensional object-forming method.
The three-dimensional object-forming apparatus includes a processing part for processing the data of a three-dimensional shape and an object-forming device for forming the three-dimensional shape based on the data.
The processing part is constituted of a three-dimensional CAD system 1 for forming the three-dimensional shape and an EWS (engineering workstation) for calculating and obtaining the data for the object-forming apparatus on the basis of the three-dimensional shape fabricated by the three-dimensional CAD system 1.
Meanwhile, the object-forming apparatus has a resin tank 10 containing a liquid photosetting resin 7. An object-forming stage 13 is provided in the resin tank 10, which is moved up and down by a lift 6. Various kinds of resin which are set by rays of light are utilizable for the photosetting resin 7, for example, epoxy resin such as epoxy acrylate, modified polyurethane methacrylate, etc.
An XY laser scanner 4 is set above the resin tank 10 for freely scanning and casting the laser light emitted from a laser 5 to the liquid surface of the photosetting resin 7 via an optical fiber 9 in the XY-direction. The laser generating device 5, XY laser scanner 4, and lift 6 are controlled by an NC device 3 based on the data of the EWS 2.
The operation of the above apparatus will now be described.
The three-dimensional CAD system 1 designs an intended three-dimensional shape and converts the data of the three-dimensional shape to an STL (storage list) format. The formatted data is sent to the EWS 2. The EWS 2 cuts the data in the STL format from the CAD system 1 at equal intervals .DELTA.Z of distance along the Z-axis vertical direction in FIG. 5) in parallel to the XY-plane, thereby representing the intended three-dimensional shape as a set of data of sectional shapes. The value of .DELTA.Z is determined by the kind of the photosetting resin being used and the power of the laser light.
Thereafter, the stage 13 is positioned by the distance .DELTA.Z below the liquid surface of the photosetting resin 7, so that the stage 13 is covered by the depth .DELTA.Z from the top thereof with the liquid resin. The XY laser scanner 4 projects the laser light to the surface of the resin 7 to trace out a shape corresponding to the lowest sectional shape. As a result, the surface resin layer is set and the lowest sectional shape is formed on the stage 13.
At this time, as shown in FIG. 7, the laser light is scanned from one end to the other end of a sectional shape 17 parallel to the Y-axis as drawn by arrows 18 while being shifted a distance 19 in a direction along the X-axis. The distance 19 is determined based on the diameter of the laser light.
When one sectional layer is formed, the stage 13 is lowered further down by the distance .DELTA.Z by the lift 6 into the photosetting resin not yet hardened, and the previously photoset layer is covered with the liquid resin of .DELTA.Z thickness. Subsequently, the XY laser scanner 4 scans the laser light to the surface of the photosetting resin 7 in a shape corresponding to a second sectional shape following the lowest sectional layer, whereby the second sectional layer is set and formed above the lowest sectional layer.
The above process is repeatedly carried out to laminate multiple photoset layers until the highest sectional layer of the desired three-dimensional shape is formed.
In the meantime, the photosetting resin used in the above three-dimensional object-forming apparatus shrinks 2-5% by volume when set by the laser light. Therefore, when the laser light is cast to the photosetting resin including an imperfectly set resin 43 in the periphery of an area 41 as in FIG. 8, the resin is hardened and turned to 42. The peripheral imperfectly set resin 43 is being supplied during this time as indicated by arrows 44 in compensation for the shrinking amount of resin. The shrinkage stress is hence hard to generate.
However, if an already set resin 45 is present in the periphery of an area 47 to be scanned by the laser light as shown in FIG. 9, while the resin in the area 47 is set and shrunken when the laser light is cast, the set resin 45 is attracted to the shrinking resin, inviting a tensile force 46. In other words, when the resin to be scanned by the laser light partially includes an already set part, the internal stress is generated from the previously set part to a successive part being hardened in accordance with the shrinkage of the resin at the setting time.
At the point in time when the laser light is cast, approximately only 98% of the photosetting resin is set, that is, it takes a great amount of time for the resin to be perfectly set. Since setting of the resin continues once the photosetting resin is set, the resin shrinks inside the product, with the stress generated.
If the laser light is cast to the photosetting resin in parallel to the X-axis or Y-axis as in the prior art, e.g., linearly in a direction of an arrow 59 as indicated in FIG. 10, an area scanned by the laser light is moved from 53 to 54 to 55 to 56 to 57, and the photosetting resin is gradually continuously set in the same direction as the scanning direction of the laser light in accordance with scanning of the laser light. Therefore, such an internal stress 58 as denoted by arrows 58 that attracts a part 51 of the resin already set to a successive part 52 is generated and accumulated.
In other words, since the internal stress 58 is generally concentrated in the same direction, namely, in a direction parallel to the X- or Y-axis according to the conventional scanning method, it is feared that the obtained product may be eventually warped or deformed.